The invention is concerned with a device with a sensor for the recognition of coins, in particular for the grading of authorised and non-authorised coins or for the determination of the coin's value.
Inspection of coins is necessary for example in automatic vending and serving machines for the recognition of a coin's value, as the counter-value should only be supplied against prescribed coins.
The known procedures for the recognition of coins analyse in particular the criteria weight, diameter, thickness and the electrical-magnetic properties of the coin's alloy. It is known that sensors in the form of foils made of polymeric material with piezoelectrical properties are used for the determination of the weight of coins (cf. G. R. Crane in IEEE Transactions on Sonics and Ultrasonics, vol. SU-25, No. 6, November 1978). However, a very large number of coins exist worldwide with approximately the same weight and very similar mechanical and physical characteristics and these are also quite easily obtainable in the era of mass tourism. In addition the forging of the above criteria of coins is simple and cheap.
This leads to the fact that coin checkers usually have to check several criteria for certain recognition of coins and that the individual tolerance limits have to be selected very closely. The device required is thus fairly sophisticated and expensive and liable to faults due to the high precision.